Audible Illusion 3A humming pop noise one channel

I thought I had a ground loop problem but everthing keeps pointing back to the Pre Amp. With volume turned down you can hear a slight hum in one speaker. When that volume control is adjusted you get a click or small pop for each adjustment. Also the power box has always had a slight hum to it which I understand others have reported this also. Any ideas what it could be, and could a local tech in the Raleigh area take a look or would it need to go back to factory?